1. Field of the Invention
The present invention relates to a process for producing a nonwoven fabric.
2. Description of the Related Art
Recently, there have been increased the kinds of machined production, such as bags and diapers, as products of nonwoven fabric. Accordingly, the machinability of a nonwoven fabric needed to be improved in order to increase the productivity of such products of nonwoven fabric. When speeds of processing machines for products of nonwoven fabric are increased, a tension in a nonwoven fabric must be increased so that the nonwoven fabric can stably run. However, when a high tension is applied to a poorly machinable nonwoven fabric, the nonwoven fabric has an increased elongation, so that the running nonwoven fabric largely fluctuates and operations of the processing machines are unstable. Accordingly, properties of products of such poorly machinable nonwoven fabric are poor.
Conventionally, 1) a method of strongly drawing a thread during spinning and 2) a method of arranging more threads in the direction of the flow of a nonwoven fabric than in the transverse direction during the spreading of fibers are employed in order to increase the fiber strength of the nonwoven fabric in the direction of the flow (hereinafter referred to as MD direction) relating to the machinability of the nonwoven fabric.
In the method of 1), thread breakage can occur during drawing. In addition, since a high fusion temperature is required when a web produced by the method of 1) is thermally embossed to the nonwoven fabric, a production speed of the nonwoven fabric must be reduced for the complete fusion of the web and, on the other hand, the fusion of the web must be incomplete so that the high-speed production of a nonwoven fabric is maintained.
The method of 2) has a drawback in that the productivity of the method is poor since the mechanical structure for achieving the method is complicated.
On the other hand, there have been proposed a process in which a web made of continuous long-fibers is drawn in the direction of the flow of the web to produce a high-strength nonwoven fabric (see Japanese unexamined patent application publication HEI.1-321962) and a process for improving the dimensional stability of a nonwoven web comprising the steps of entangling filaments of the nonwoven web by means of a liquid flow and subsequently drawing the nonwoven web in a predetermined range in at least one direction (see Japanese unexamined patent application publication SHO.59-204960).
In the process of Japanese unexamined patent application publication HEI.1-321962, a problem that the nonwoven fabric winds about a roller may occur since the drawing temperature is high.
In the process of Japanese unexamined patent application publication SHO.59-204960, there is a problem in that the productivity is poor since the step of entangling filaments by means of the liquid flow is required.
An object of the present invention is to provide a process for producing a nonwoven fabric of a superior machinability.